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OXIDISED OILS  (BLOWN OILS)

445

OXIDISED   OILS
(Blown Oils)

These are obtained by passing a current of air through a fatty oil at a
temperature of about 70-120° until the oil becomes thick and viscous like
castor-oil. Col/a, cottonseed, maize, foot and fish oils are usually employed
for this purpose.

In general, blown oils are dense, viscous, reddish-brown liquids with a
special odour (of boiled oil). In comparison with the corresponding original
oils, they have, high specific gravities, refractivities and saponification
numbers and low iodine numbers (see Table, p. 446). Further, they contain
marked quantities of hydroxy-acids, and it is characteristic of them that
they furnish deep brown fatty acids (almost black with blown fish oils),
only partially soluble in ether.

Analysis of these products is concerned principally with the two following
cases :

1.  Origin of the Blown Oil.—It is somewhat difficult to state the
nature of the original oil from which a blown oil is prepared, since the specific
colour reactions  no  longer hold.   An approximate orientation may be
obtained by means of the following criteria.

The fatty acids of oxidised colza oil are liquid and their lead salts are
mostly soluble in ether.

The fatty acids of oxidised cottonseed oil are solid and their lead salts
partially soluble in ether.

The fatty acids of oxidised fish oils are blackish and saponification of
these oils yields a black, pitchy substance insoluble in potash, alcohol or
ether and similar to the linoxyn of linseed oil. This does not occur with
blown vegetable or foot oils. Blown fish oils are the ones showing the
greatest density accompanied by the highest iodine number.

Oxidised foot oils exhibit a specific gravity equal to that of oxidised
vegetable; oils but a. less iodine number.

2.  Mixtures of Blown Oils with Mineral Oils.—Mixtures of heavy
mineral oil and oxidised oil (about 5-30%) form good lubricants for marine
engines.

Such products are. recognisable by the smell and by the following test:
10 grams of the oil are saponified with 25 c.c. of alcoholic potash in the
usual way, heating for half an hour on the water-bath in a reflux apparatus
with frequent shaking. Without evaporating the alcohol, the whole is
transferred to a separating funnel, diluted with 150 c.c. of water, shaken
gently and carefully and left to stand until sharp separation into two layers
takes place, the lower aqueous layer being then run off and the supernatant
mineral oil collected separately (with the help of a little ether), dried and
weighed.

On the other hand, the aqueous liquid is acidified and the fatty^acids
separated : these should exhibit the characters of the acids of oxidised
oils, that is, they should be brown and not completely soluble in ether
(see above).ibit cracking and should become detached in scales when scraped with a